linux-kernel - Re: 2.6.25.3: serial problem (minicom)

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Message-ID: <alpine.LNX.1.00.0806200314190.1258@hani.compact.internal>
Date:	Fri, 20 Jun 2008 06:22:20 -0500 (CDT)
From:	"R.L. Horn" <lists@...tcheap.org>
To:	Hans-Peter Jansen <hpj@...la.net>
cc:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.25.3: serial problem (minicom)

On Fri, 20 Jun 2008, Hans-Peter Jansen wrote:

> Alan, I got to test this by applying the changeset (Olivier, many thanks
> for your valuable hint, I'm sure, I will reuse this knowledge soon), to
> the otherwise unchanged kernel, but unfortunately, it doesn't solve my
> issue.
>
> A different patch must have changed the behavior/state of some RS232 lines
> in the 2.6.25 time frame,

There was a deliberate change in DTR behavior, though I'm not up on the 
details.  If you have a copy of 2.6.25.something handy and want to check 
that that's the problem, you might look at drivers/serial/serial_core.c. 
Round about line 2160 (in uart_configure_port()), you'll see:

   /*
    * Ensure that the modem control lines are de-activated.
    * keep the DTR setting that is set in uart_set_options()
    * We probably don't need a spinlock around this, but
    */
   spin_lock_irqsave(&port->lock, flags);
   port->ops->set_mctrl(port, port->mctrl & TIOCM_DTR);

Change the last line to:

   port->ops->set_mctrl(port, 0);

which reverts to 2.6.24 behavior.

If your problem isn't resolved here, please contact me off-list with some 
details about your receiver, ntpd version, etc. and I'll look into it 
further.  I've been thinking about building a WWVB doodad, and a solution 
to this might save me some grief later on.

> As another data point: using a usb <-> rs232 converter, the dcf device 
> got back to life again. It still doesn't work in its entirety, but at 
> least, some data arrives in ntpd. Expected is something similar to:
> -#--#-#####-###--D--S124--2-p------p-----21-4-24-----8-- (incomplete)
> but it reads:
> ###############RADMLS1248124P124812P1248121241248112481248P
> thus, obviously it doesn't get any 0 values back (displayed as - above).

That looks like a hardware problem.  Odds are, something here (and it 
could be the USB<->RS232 converter or the DCF receiver or both) either 
isn't up to RS-232 specs or the receiver is making unfounded assumptions 
about the DTE port.  In particular, I'd want to know the mark/space 
voltages coming out of that USB thingy.
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